Synergistic extraction of Ce(IV) and Th(IV) with mixtures of Cyanex 923 and organophosphorus acids in sulfuric acid media

Selective Extraction of Thorium(IV) from Uranium and Rare Earth Elements Using Tetraphenylethane-1,2-diylbis(phosphoramidate)

Tetraphenylethane-1,2-diylbis(phosphoramidate) in conjugation with a room temperature ionic liquid in chloroform medium is reported for the first time in the liquid-liquid extraction of thorium (Th). The extracted Th(IV) is collected as a white solid in the organic medium, thereby facilitating its easy separation. A high distribution ratio (D) of (12.4 ± 0.1) × 10³ in 2-8 mol L^-1 acidity range and high decontamination factors (α) of Th(IV) from uranium, lanthanides, and a number of transition elements makes this extraction process versatile and selective. A number of experimental investigations in synergism with extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) studies are interpreted to confirm the structure of the chelated complex. A 1:2 metal/ligand complex in which the two oxygen and two nitrogen atoms of each bis(phosphoramidate) molecule satisfying the eight coordination sites of Th(IV) is found to be formed. The extracted white solid thorium complex is easily converted to ThO₂ after washing and heating at 1300 °C under O₂ atmosphere. This work is expected to find direct application in the thorium fuel cycle, especially in the mining process of thorium from its ores and in the separation of fissile ²³³U from fertile ²³²Th in irradiated fuel.

Solvent Extraction of Lanthanides(III) in the Presence of the Acetate Ion Acting as a Complexing Agent Using Mixtures of Cyanex 272 and Caprylic Acid in Hexane

A new extraction system containing a mixture of Cyanex 272 and caprylic acid is proposed for the extraction and separation of lanthanides(III). It was shown that this system possesses a high level of extraction ability and capacity. The extraction of lanthanides(III) from chloride-acetate and nitrate-acetate media was investigated on an example of La(III). The composition of the extracted species was confirmed, based on the analysis of lanthanum(III) extraction isotherms. In the case of acetic-acetate aqueous solutions, a decrease in lanthanum(III) extraction efficiency was observed, due to the decreasing equilibrium pH of the aqueous phase in accordance with the cation-exchange mechanism. The composition of the synergistic mixture of Cyanex 272-caprylic acid established demonstrates highly efficient separation of rare-earth metal ions.

Selective Extraction and Complexation Studies for Thorium(IV) with Bis-triamide Extractants: Synthesis, Solvent Extraction, EXAFS, and DFT

Three octyl-extended bis-triamide extractants (L1-L3) were designed and synthesized for the selective solvent extraction of Th(IV) over U(VI) in a kerosene-HNO₃ system. L1 and L2 exhibited good extraction property and selectivity toward Th(IV) over U(VI) and reached extraction equilibrium within 10 min. In a wide range of a HNO₃ concentration from 0.1 to 3.0 M, the separation factor of Th(IV) over U(VI) (SF_Th/U) of L1 and L2 ranged from 12.1 ± 1.6 to 123.0 ± 20.2 and 15.2 ± 2.4 to 88.1 ± 14.9, respectively. Slope analysis indicated that Th(IV) was extracted as different species under different HNO₃ concentrations, in which the slopes were 2.08 ± 0.20, 1.61 ± 0.03, and 1.54 ± 0.03 for L1 and 2.37 ± 0.22, 2.07 ± 0.17, and 1.76 ± 0.18 for L2 under 0.1, 1.0, and 3.0 M HNO₃, respectively. A continuous variation method (Job plot) illustrated a 1.5:1 ligand/thorium (L/Th) ratio in a methanol phase, indicating that L1/L2 and Th(IV) could form mixed 1:1 and 2:1 L/Th extracted complexes. Extended X-ray absorption fine structure (EXAFS) and density functional theory (DFT) calculations revealed that the extracted complexes of L1 and L2 with Th during the extraction process at 0.1 M HNO₃ were [2L1·Th·3(NO₃)]⁺ and [2L2·Th·3(NO₃)]⁺.

A safer and cleaner process for recovering thorium and rare earth elements from radioactive waste residue

Rare earth elements (REEs) have attracted widely attentions because of their excellent properties, however, radioactive waste residue generated during the REEs production has created serious environmental problems. This study aimed to develop a safer and cleaner technology, including residue leaching, thorium (Th) separating and REEs recovering, for the proper disposal of radioactive waste residue from ion-absorbed rare earth separation industry to reduce the environmental hazards. First, the chemical composition of residue was analyzed. Then, the leaching factors such as acid type, acid concentration and liquid-solid ratio were investigated and a multi-step leaching process was proposed to improve acid utilization and the leaching of REEs. After the multi-step leaching with HCl, the total leaching efficiency of REEs and Th were higher than 98.14% and 99.07%, respectively. Next, a commercial extractant of sec-octylphenoxy acetic acid (CA-12) was used to separate Th and enrich REEs from the residue leachate. The extraction factors of CA-12 toward Th were investigated in detail and a fractional extraction for separating Th and enriching lanthanides from the leachate of residue was carried out, showing that the separation efficiency of Th was higher than 99.53% and the concentration of lanthanides in the concentrated solution was 223.19 g L^-1.

Synthesis and characterization of a new ion-imprinted polymer for the selective separation of thorium(iv) ions at high acidity

A new ion-imprinted polymer (IIP), which was synthesized with bis(2-methacryloxyethyl) phosphate as functional ligand and Th⁴⁺ as a template ion, can be used in high acidity environment.